Third-party airfare search websites like Google Flights can make it easy to compare flights across multiple airlines. Even if you prefer to buy directly from the airline, these tools allow you to compare factors like departure time, the duration of the flight and the price across several major airlines.

That is, except one, glaring omission among U.S. airlines, according to a NerdWallet analysis of the tool: Southwest Airlines.

Google Flights displays Southwest departure and arrival times, flight duration and carbon dioxide emissions. However, it states “Price unavailable,” accompanied by a link to Southwest’s website, if comparison shoppers want to see the price.

Other online travel agencies such as Expedia or Kayak aren’t much better. Expedia doesn’t display Southwest flights at all. For example, in a search of nonstop flights between Denver and San Francisco departing in March 2023, Expedia displays only United Airlines and Frontier Airlines, even though Southwest also operates that route.

Kayak similarly omits Southwest flight options, only displaying a Southwest ad. It doesn’t allow shoppers to narrow results by Southwest, despite including smaller carriers like Allegiant Air and Sun Country Air in its filter tool.

For travelers open to considering flights across multiple airlines, understanding how Southwest fits in is a real headache. They may be losing out not just on cost comparisons, but the knowledge that there may be a more convenient flight time or route on Southwest versus the other airlines.

Airfare shoppers comparing flights on Google Flights have to navigate to a separate page on Southwest’s website to reveal the price rather than reviewing options on a single screen.

That might not be all that annoying to do with one airline, but if every airline’s fare costs are not displayed — even if departure times are — comparison shopping becomes a real headache.

Some third-party travel search engine customers might not even realize Southwest is an option, perhaps missing out on a more desirable departure time or flight length. That means they’d also miss out on Southwest’s other perks, such as free checked bags and a flexible change and cancellation policy.

Going back to the flight route between Denver and San Francisco, the cheapest Frontier option available is $89, and the United flight is $195. Meanwhile, nonstop Southwest flights for the same destinations ranged from $163 to $206.

Southwest is sometimes more expensive than competitors, but these prices only paint a portion of the financial picture. For example, United’s fares don’t include free bags (your first United checked bag typically costs $35), while Southwest lets you check two for free. Those price differences aren’t as easy to display on comparison tools.

In most cases, it’s not the online travel agency giving Southwest the cold shoulder and refusing to display the airline’s flight information. Southwest doesn’t allow other websites to display its airfares. 

“Southwest Airlines has a unique and customer-friendly business model in the United States which includes making our fares available to the general public only on Southwest.com,” Southwest spokesperson Tiffany Valdez said in an email to NerdWallet. “Unlike most other airlines, Southwest does not use online travel agencies to market or sell tickets. ”

Google Flights requires a partnership with either the airline itself or a data provider with access to an airline’s fares in order to display prices to consumers. Currently, the search engine doesn’t have such an arrangement with Southwest. But the folks there say they’d post the airline’s airfares if they could.

“​​Travelers ought to have a comprehensive view of flight options and airfares, so we’ll happily work with any airline or relevant data provider to make this possible,” says James Byers, group product manager at Google Flights. Byers says Google Flights receives a high volume of feedback from users indicating that they’d like to see full pricing information for all airlines.

Expedia shared a similar sentiment.

“We’d welcome the opportunity to display Southwest flights,” said Julie Kyse, vice president of global air partnerships for Expedia Group, by email.

It’s common practice across most industries for the selling party to pay a commission to the referring party. For example, Amazon’s affiliate program pays between 1% and 5% of the price of most items sold to shoppers who visit its site through affiliate links. Similarly, hotels commonly offer commissions to travel agents, with Hilton, Hyatt and IHG among the big hotel brands paying up to 10% commission on most room revenues. 

To avoid paying that cut to referrers, some hotels offer incentives to encourage direct bookings. For example, Ovolo Hotels promises the lowest room rates on its site, plus free breakfast, laundry and snacks for direct bookings — something you won’t get if you go through a third party.

Expedia’s business model centers around earning commissions or ticketing fees from the travel supplier and traveler. According to its latest quarterly earnings release in November 2022 for the third quarter of 2022, Expedia Group earned $100 million in revenue solely from airfares.

But while Expedia typically takes a cut, Google Flights does not. In January 2020, Google Flights made it free for all partners to participate in its display. Google currently doesn’t charge airlines for any traffic or bookings made through Google Flights.

There’s not a lot you can do except visit Southwest’s website and note those prices against prices for all the other airlines displayed on third-party travel sites. Or bypass a search tool and head to the Southwest site directly, especially if it’s your favorite airline.

Of course, you could also voice your complaints to Southwest by contacting the airline directly. And sometimes the easiest way to make a statement is with your dollars, which might be booking on another airline if the whole lack-of-comparison-shopping bothers you.

Unlike other airlines that nickel and dime for services like checking bags and changing flights, Southwest’s lack of hidden fees is refreshing — so much so that we consider it the airline with the lowest fees.

But when it comes to folks looking to comparison shop, Southwest’s policies can incite unnecessary turbulence.